The present invention relates to an axle bearing assembly for supporting a wheel of an automobile, and particularly it relates to an axle bearing assembly used for wheels of the type in which a raceway surface is formed directly on the axle, and to a method of measuring bearing clearances.
As an example, in a conventional axle bearing assembly shown in FIG. 15, the inner periphery of an outer ring 21 is formed with two rows of raceway surfaces 21a and 21b, and a raceway surface 23a opposed to the raceway surface 21b is formed on the outer periphery of an inner ring 23 while a raceway surface 22a opposed to the raceway surface 21a is directly formed on the outer periphery of an axle 22. The outer ring 21 is integrally formed around its outer periphery with a flange 21c to be fixed to the body of an automobile or the like, while the axle 22 is integrally formed around the outer periphery of the end thereof with a flange 22g for mounting a hub bolt 27 thereon. Further, the axle 22 is formed on substantially the central outer periphery thereof with the raceway surface 22a and also with a press-fit portion 22c continuous therewith through a shoulder portion 22b and adapted to have the inner ring 23 press-fitted thereon. The inner ring 23 is press-fitted on the press-fit portion 22c of the axle 22 and fixed in position by a nut 26 screwed on the end of the axle 22.
In this connection, in this kind of bearing assembly, considering the rolling life, rigidity, and fretting of the bearing, the advantageous use of the bearing is with a negative axial bearing clearance, i.e., with a predetermined preload; however, since it is difficult from the viewpoint of controlling the clearance to measure a negative bearing clearance, it has been common practice to predetermine an initial bearing clearance by allowing for a decrease in the bearing clearance by press-fitting the inner ring 23 on the press-fit portion 22c or by tightening by means of the nut 26. That is, the tightening torque to be applied to the nut 26 corresponding to the desired amount of preload is preset, and the inner ring 23 is forced toward the shoulder portion 22b of the axle 22 until the tightening torque on the nut 26 reaches this present value. Accordingly, if such preload (hearing clearance) control means is used, it is essential that upon completion of the press fitting, a spacing W be present between the front face of the inner ring 23 and the shoulder portion 22b of the axle 22.
Generally, in a double row angular contact ball bearing having a pair of inner rings, since the relative position between the pair of inner and outer rings determines the bearing clearance (amount of preload), the bearing clearance (negative bearing clearance) can be measured, e.g., in the manner shown in FIG. 16. That is, with the pair of inner rings 33 held by a shaft member 32 for measurement so as to reduce the axial bearing clearance of the bearing to zero, compressed air X is blown out of the spacing h between the inner rings 33 through an air passage 32a provided in the shaft member 32, and then the spacing h is found from the detected value of the back pressure of the compressed air X or the like; thus, the negative bearing clearance (=h) which is present upon completion of the assembly can be found. However, in a bearing assembly as shown in FIG. 15, since the bearing clearance is determined by the amount of press-fitting of the inner ring 23 on the axle 22, it is impossible to use the above-described measuring method as it is. Herein lies the reason why the indirect clearance control has been made in this kind of bearing by the tightening torque on the nut.